---
title: 'Senior Backend Engineer, External at Horizon3 AI'
canonical: 'https://feeny.ai/job/senior-backend-engineer-external-horizon3-ai-united-states-0k8435awcpgq'
type: 'job'
last_seen: '2026-11-07'
---

# Senior Backend Engineer, External at Horizon3 AI

- **Company:** [Horizon3 AI](https://feeny.ai/companies/horizon3-ai)
- **Location:** United States
- **Employment:** full-time
- **Work type:** remote
- **Posted:** 2026-10-19
- **Last confirmed live:** 2026-11-07
- **Apply:** https://jobs.ashbyhq.com/horizon3ai/2305cc3b-7292-45f3-8264-e4a8c5c41511

## Job description

Get to Know Us Horizon3 is a fast-growing, remote cybersecurity company dedicated to the mission of enabling organizations to proactively find and fix and verify exploitable attack vectors before criminals exploit them. Our flagship product, the NodeZeroTM platform, delivers production-safe autonomous pentests and other key assessment operations that scale across the largest internal, external, cloud, and hybrid cloud environments. NodeZero has been adopted by organizations of all sizes, from small educational institutions to government agencies and Global 100 enterprises. It is used by ITOps/SecOps teams, consulting pentesters, and MSSPs and MSPs. We are a fusion of former U.S. Special Operations cyber operators, startup engineers, and formerly frustrated cybersecurity practitioners. We're committed to helping solve our common security problems: ineffective security tools, false positives resulting in alert fatigue, blind spots, "checkbox” security culture, cybersecurity skills shortage, and the long lead time and expense of hiring outside consultants. Collectively, we are a team of learn it alls, committed to a culture of respect, collaboration, ownership, and results.

## What You’ll Do

As a Senior Backend Engineer on the External Attack team, you'll contribute to the full set of backend services that power NodeZero's external pentesting capabilities, from architecture and development through deployment and production operations. You'll own parts of our core API, data processing and ETL pipelines, datalake, graph, along with the container orchestration and cloud infrastructure beneath it all. You'll be accountable for the performance, scalability, and uptime of several of these services, and you'll be a key contributor to user-facing product launches and platform stability.

## Responsibilities

- Design, build, and maintain features in our core Python API, with a focus on performance, correctness, and maintainability.
- Design, build, and operate workflow orchestration for large-scale, long-running workloads using tools such as Prefect or Temporal, including scheduling, retries, idempotency, state management, and failure recovery.
- Build orchestration that scales reliably across many concurrent workflows, with clear visibility into progress, failures, and throughput.
- Comfort reading and untangling unfamiliar, complex SQL, and the judgment to optimize or refactor it safely in production.
- Build and operate high-throughput data processing and ETL pipelines that turn large volumes of raw assessment data into reliable, queryable datasets.
- Contribute to datalake architecture on AWS, including storage layout, partitioning, schema evolution, and query performance.
- Deploy and manage services on Kubernetes, and take part in cluster operations, release management, and capacity planning.
- Develop and extend GraphQL and graph-based APIs that let product components and customers explore complex relationships in their data.
- Own the observability, uptime, and scalability of the services you build, including metrics, tracing, alerting, and on-call participation.
- Partner with frontend engineers, product managers, and designers to turn backend capabilities into a clear, responsive user experience.
- Contribute to systems architecture decisions and write design docs that help the team move quickly with shared understanding.
- Collaborate with frontend team members to present data in a clear and user-friendly format, enhancing the product's user experience.

## What You’ll Bring

- The ability to own and manage concurrent initiatives, with sound judgment in prioritization and time management.
- A self-driven approach: you can conceive and implement solutions on your own and with a team.
- A reliability mindset for distributed work: you design for retries, partial failure, and recovery, and you debug asynchronous systems methodically.
- A strong desire to keep learning new technologies in a fast-paced Agile environment.
- Excellent analytical and problem-solving skills, clear communication, and attention to detail.
- A bias toward operational ownership: you care how your code behaves in production
- Strong technical writing for design docs, runbooks, and API documentation.
- Effective collaboration with designers, developers, and product managers.

Required Education / Experience

- Bachelor's Degree in Computer Science, Computer Engineering or related field.
- 7+ yrs professional software engineering experience using modern object-oriented or functional languages (Python, Java, Go, Scala, C++, TypeScript, etc).
- Experience building and running workflow orchestration or distributed task-processing systems in production (for example Prefect, Temporal, Airflow, Celery, or similar).
- Hands-on experience designing and building high-throughput data processing systems and ETL pipelines.
- Experience building applications on cloud computing platforms such as AWS, Azure, GCP, using container technologies such as Docker and Kubernetes.

What Sets You Apart

- Deep Kubernetes experience, including managing deployments and clusters and troubleshooting production workloads.
- Experience with durable-execution or workflow engines such as Temporal or Prefect, including designing workflows that are resilient, observable, and easy to evolve.
- Experience building GraphQL backends and working with graph databases
- A track record of owning observability, uptime, and scalability for production systems (for example Datadog, Prometheus, or OpenTelemetry).
- Systems engineering and architecture experience with datalakes and the cloud services around them.
- Experience building platform capabilities or internal tooling that other engineering teams rely on.
- Experience in cybersecurity or with attack surface and vulnerability data.

Only US persons can interview for this role due to security clearance requirements by our customer(s) and/or vendor(s). Employee must be eligible for and successfully secure a US Federal Security Clearance as a condition of employment.

Travel Required We are a fully remote company, and this job may require up to 5% of travel to be successful.

## Perks of Horizon3

- Inclusive Team: We value diversity and promote an inclusive culture where everyone can thrive.
- Growth Opportunities: Be part of a dynamic and growing team with numerous career development opportunities.
- Innovative Culture: Work in a collaborative environment that encourages creativity and out-of-the-box thinking.
- Hybrid & Remote Work: We embrace a mix of remote and hybrid work models depending on role and location, including our Chicago office, where some roles require regular in-office presence.
- Competitive Compensation: We offer competitive salary, equity and benefits. Our benefits include health, vision & dental insurance for you and your family, a flexible vacation policy, and generous parental leave.

## Compensation and Values

At Horizon3, we believe that our people are our greatest asset, and our compensation philosophy reflects this core value. We are committed to fostering an environment where all employees feel valued, respected, and rewarded for their contributions. Our compensation structure is designed to be fair, competitive, and transparent, ensuring that every team member is recognized and compensated equitably across roles, levels, and locations. In accordance with various State’s transparency regulations, we provide the following salary range information for this position:

- Base salary range: $199,750 - $235,000 annually. The exact salary will be determined based on the selected candidate’s location, qualifications, experience, and relevant skills.
- Additional compensation: All full-time roles are eligible for an equity package in the form of stock options.

You Belong Here Horizon3 is not just an equal opportunity employer - we are a community that values diversity, equity, and inclusion as fundamental principles of our culture and success. We are dedicated to fostering a workplace where everyone feels welcome and respected, regardless of race, color, religion, sex, national origin, age, disability, veteran status, sexual orientation, gender identity or expression, genetic information, marital status, or any other legally protected status by law. Our commitment to diversity and inclusion means we strive to attract, develop, and retain a workforce that reflects the varied communities we serve. We believe that diverse perspectives drive innovation and strengthen our ability to create cutting-edge cybersecurity solutions. At Horizon3, every team member is valued and supported in an environment that encourages personal and professional growth. We welcome candidates from all backgrounds and experiences, and we encourage all qualified individuals to apply. Come be a part of Horizon3, where your unique contributions are recognized, and your potential is limitless.

Other Duties Please note this job description is not designed to cover or contain a comprehensive listing of activities, duties or responsibilities that are required of the employee. Duties, responsibilities, and activities may change at any time with or without notice.

Application Note In any materials you submit, you may redact or remove age-identifying information such as age, date of birth, or dates of school attendance or graduation. You will not be penalized for redacting or removing this information.

## About Horizon3 AI

## Company Overview
- **One-liner**: Horizon3.ai provides an autonomous penetration testing platform (NodeZero) that safely hacks production environments to identify and fix exploitable attack paths using AI.
- **Entity Type**: Private (Series D – latest funding round in 2026, led by Prosperity7 Ventures)
- **Headquarters**: San Francisco, California, United States (447 Battery Street, San Francisco, CA 94111)
- **Founded**: 2019
- **Founders**: Snehal Antani (Co-Founder & CEO); founded by a mix of US Special Operations, US National Security, and cybersecurity industry veterans

## Core Business
- **Primary industry**: Cybersecurity (autonomous penetration testing, vulnerability management, continuous security validation)
- **Target customers**: B2B – large enterprises, Fortune 100, government agencies (NSA, CISA), healthcare providers, financial services, manufacturing, education, public sector
- **Mission**: “Turn the map around” – using the attacker’s perspective to help enterprises prioritize defensive efforts. The company aims to shift the advantage from attackers to defenders by fighting AI with AI.

## Products & Services
- **[NodeZero®](https://horizon3.ai/)**: Autonomous penetration testing SaaS platform. Safely runs real attack techniques in production environments (no agents, no disruption). Discovers and chains exploitable vulnerabilities, misconfigurations, harvested credentials, and dangerous defaults across external, identity, on-prem, cloud, and Kubernetes attack surfaces. Also includes Active Directory password auditing and phishing impact testing. Continuously validates fixes and repeats autonomously.

## Market Standing
- **Valuation**: Not publicly disclosed
- **Key Metrics**: 
  - Annual Revenue: **$35.5M** (per LinkedIn)
  - Total Funding: **$187M** (per LinkedIn) / **$181M** (per CB Insights – conflicting reports; both cited)
  - **225,000+** production-safe tests completed
  - **5,000+** customers
- **Notable Investors/Partners**: 
  - SignalFire (lead in Seed, Series A, Series B)
  - Craft Ventures (lead Series C)
  - Prosperity7 Ventures (lead Series D – 2026)
- **Growth Signals**:
  - Ranked **#1 in Security** on the 2025 Inc. 5000 list
  - **#3 overall** on the 2025 Deloitte Technology Fast 500
  - Fast Company’s **Most Innovative Companies** (2026) – #1 in Security
  - Named to the **Fortune Cyber 60** (2023 & 2025)
  - Two-time **Black Unicorn Award** winner
  - Headcount grew **115.5% YoY** to 341 employees (LinkedIn)
  - Active job postings up **168.2% YoY**; operates in 14 countries

## Competitive Advantages
- **AI-driven autonomous testing** that learns from hundreds of thousands of tests and uses the right AI (ML, GenAI) for each problem – delivers evidence-based results with **zero hallucinations**.
- **Production-safe** – zero downtime across all production tests, trusted by the world’s most sensitive high-security environments (NSA, CISA, Fortune 10, major healthcare).
- **No agents required** – fully self-service SaaS, safe to run continuously.
- **Real attack techniques** – not a scanner; shows actual attacker paths and impact.
- **Rapid verification** – instantly confirms fixes and repeats the cycle, enabling a continuous validation loop.

## Strategic Focus
- **Continuous validation** – driving a loop of test-fix-verify-repeat autonomously.
- **Fighting AI with AI** – building NodeZero to operate at machine speed against AI-powered attacks.
- **Global expansion** – already in 14 countries, with active hiring in EMEA, APAC, and the Americas.
- **Scaling the team** – 59 active job postings (as of mid-2026), with emphasis on engineering, sales, and customer success roles.

## Why Work Here
- **Culture**: Rated **5.0/5.0 on LinkedIn** (76 reviews) with perfect scores for Culture (5.0), Career (4.9), Compensation (4.7), and Work-Life (4.6). Described as a “kick-ass organization hell bent on disrupting an industry” with a team of “motivated learn-it-alls.”
- **Work Policy**: Remote-friendly (most roles listed as remote, HQ in San Francisco, CA). Offers flexibility across time zones.
- **Notable Perks** (from Built In and LinkedIn):
  - Comprehensive healthcare (medical, dental, vision, FSA)
  - Life insurance, disability insurance
  - 401(k) with company matching
  - Equity and employee stock purchase plan
  - Generous parental leave and family medical leave
  - Performance bonuses
  - Job training, conferences, and customized development tracks
  - Promotion policies and career growth support
- **Engineering Culture**: Built by US Special Operations and National Security veterans. Emphasis on high autonomy, real-world impact, and cutting-edge AI/security work. “If you want to be part of a kick-ass organization hell bent on disrupting an industry and keeping attackers at bay, let’s talk.”

## Sources
1. [horizon3.ai – Homepage](https://horizon3.ai/)
2. [horizon3.ai – About/Team](https://horizon3.ai/about-us/)
3. [LinkedIn – Horizon3.ai Company Page](https://www.linkedin.com/company/horizon3ai)
4. [Built In – Horizon3.ai Careers & Perks](https://builtin.com/company/horizon3ai)
5. [CB Insights – Horizon3.ai Profile](https://www.cbinsights.com/company/horizon-3-ai)

## Other roles at Horizon3 AI

- [Director of Engineering, Threat Research](https://feeny.ai/job/director-of-engineering-threat-research-horizon3-ai-united-states-0fsq2qg04cee) — United States
- [Senior Attack Engineer, GCP](https://feeny.ai/job/senior-attack-engineer-gcp-horizon3-ai-united-states-p7dypj66skxv) — United States
- [Senior Attack Engineer, Kubernetes](https://feeny.ai/job/senior-attack-engineer-kubernetes-horizon3-ai-united-states-8bbsrmqpg924) — United States
- [Senior Attack Engineer, OCI](https://feeny.ai/job/senior-attack-engineer-oci-horizon3-ai-united-states-06y0k0t6a5p9) — United States
- [Staff Backend Engineer, Internal](https://feeny.ai/job/staff-backend-engineer-internal-horizon3-ai-united-states-eccvzb53mpb7) — United States
- [Senior Sales Engineer (SLED)](https://feeny.ai/job/senior-sales-engineer-sled-horizon3-ai-united-states-agqan5xzy6d6) — United States
- [Research Staff, Adversarial Intelligence](https://feeny.ai/job/research-staff-adversarial-intelligence-horizon3-ai-united-states-xxx9ghesv6ha) — United States
- [Engineering Manager, Internal Attack](https://feeny.ai/job/engineering-manager-internal-attack-horizon3-ai-united-states-tx9j8q1pkfsx) — United States
- [Senior Account Executive, SLED - New York](https://feeny.ai/job/senior-account-executive-sled-new-york-horizon3-ai-new-york-2d49m7hyp482) — New York, NY
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